Depth Buffer Trouble

I''m using gluUnProject to find the object coords of a given pixel on the screen, using the x and y coords of a mouse cursor and the z element from the depth buffer. As it happens my call to glReadPixels simply isn''t returning a value which in turn throws off the subsequent call to glUnProject. Here''s the actual call: glReadPixels ( mouseXpos, mouseYpos, 1, 1, GL_DEPTH_COMPONENT, GL_DOUBLE, &mouseZpos ); As a special note I have enabled GL_LEQUAL depth testing (although I toggle it on and off to draw my interface with blending - I only turn it off after I try to make the call above). This one has me stumped, since the procedure is pretty straightforward. ----------------------------- Mice are an excellent source of mice.